Field of the Invention
The present disclosure relates to a transformable device and a display device including the same and, more specifically, to a multilayer transformable device having enhanced bending ability and a display device including the same.
Discussion of the Related Art
Recently, various display devices including liquid crystal displays (LCDs) and organic light-emitting diodes (OELDs) have touch functionality, as users desire to conveniently interact with their display devices. In this regard, researches have been continuously conducted into a transformable device and its integration into a flexible display device that can provide direct and various touch feedbacks to users.
In general, a conventional display device has used a vibration motor such as an eccentric rotating mass vibration motor (ERM) or a linear resonance actuator (LRA) as a transformable device. The vibration motor is designed to vibrate the whole display device, and thus has a problem in that its mass body needs to be increased in size to increase its vibration power. In addition, the vibration motor has disadvantages in that frequency modulation for adjusting a level of vibration is difficult, a speed of response is significantly low, and the vibration motor is not suitably used for a flexible display device.
To address these issues, a shape memory alloy (SMA) and electro-active ceramics (EAC) have been developed as materials for a transformable device. However, the SMA has a low speed of response and a short lifespan, and is opaque, and the EAC is fragile. Thus, there has been difficulty in applying the SMA and the EAC to a display device, in particular, to a flexible display device.
A transformable device technology using an electro-active polymer (EAP) has recently been receiving attention in the industry. The EAP refers to a polymer that can be deformed by an electrical stimulation. More particularly, the EAP can repeatedly expand, contract and bend by an electrical stimulation. Among various types of EAPs, a ferroelectric polymer and a dielectric elastomer have been mainly used. Examples of ferroelectric polymer are polyvinylidene fluoride (PVDF) and P(VDF-TrFE)(Poly(VinyliDene Fluoride)-trifluoroethylene), and examples of dielectric elastomer are a silicone-based polymer, a urethane-based polymer, an acrylic-based polymer, and the like. A transformable device including the EAP as an electro-active layer has been manufactured and attached to a flexible display panel to implement diverse bending of a display device.
However, such a transformable layer that uses only one transformable layer such as the EAP may have difficulty in implementing sufficient driving displacement. When a thickness of the transformable layer is increased to enhance driving displacement, its bending ability may become restricted due to its increased thickness. Moreover, the increased thickness of the transformable layer may require high driving voltage, and thus, may not be suitable for mobile displays.